The present invention, generally, relates to the field of electron spin resonance (ESR) dosimetry.
More specifically, the invention relates to a probehead for an electron spin resonance dosimeter reader, comprising a resonator and an insert extending into the resonator having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance.
Still more specifically, the invention relates to a probehead for an electron spin resonance dosimeter, comprising a resonator, an insert extending into the resonator having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, and a pressurized air unit for blowing the sample out of the resonator after completion of a measurement.
Moreover, the invention is related to a sample substance for an electron spin resonance dosimeter, comprising a chromium-doped magnesium oxide (Cr:MgO).
A probehead of the type of interest in the present context is disclosed in document JP 01 138 484 A.
In the industrial practice, it becomes more and more customary to irradiate products of any kind. For example, various products are irradiated for disinfection purposes or for increasing their durability, respectively. A typical example is the field of hygiene articles, for example baby""s diapers. During production, such diapers are packed in batches and are then irradiated batch by batch in order to put them at the customer""s disposal in a germ-free condition. It is common practice to convey the articles to be irradiated batch by batch past a source of irradiation, wherein several passes may be provided in order to achieve a predetermined dose of irradiation.
Further, it is a well-established practice to irradiate products and articles in order to exterminate unwanted organisms. In practice this happens for example in connection with food-stuffs, for example spices which are sometimes affected by pathogenic germs and, prior to being processed and distributed, must be treated accordingly.
Still another field of application is the prophylactic irradiation of articles of many kinds in connection with the use of biologic warfare agents if, for example, pieces of mail must be treated as a precautionary measure, because it must be expected that certain pieces of mail containing pathogenic germs are mailed in connection with terrorist attacks.
In all these and many other applications of irradiation, it is, however, desired to properly measure the amount of irradiation and, as the case may be, to document same. This holds true basically independent of the kind of irradiation (gamma rays, electron rays, etc.).
For that purpose, corresponding measuring instruments, dosimeter substances, packaging methods for dosimeter substances and pertinent standards have been developed under the general term xe2x80x9cdosimetryxe2x80x9d. In the U.S., for example, the American Society for Testing and Materials has developed and published a standard E 1607-96 xe2x80x9cStandard Practice for Use of the Alanine-EPR Dosimetry Systemxe2x80x9d. Dosimetry methods are today certified by various official and other institutions. For that purpose, it is necessary to be able to follow-back measuring samples, i.e. to provide a complete documentation.
Conventional dosimeters, as are used, for example, for protecting people in installations where work is done with rays of various kinds, essentially consist of a section of a normal commercial photographic film which becomes blackened under the action of an irradiation. The film sections are developed after a certain period of time has lapsed, and are then evaluated optically, wherein the amount of blackening of the film is a measure for the irradiation dose received. Such film dosimeters are still today used on a broad scale in connection with the measurement of irradiation doses in industrial irradiation processes.
Film dosimeters, however, have the disadvantage that they are relatively complicated in their handling and evaluation. Further, one has found out that they are not stable over an extended period of time. A fast and reliable measurement of irradiation values is, therefore, as much impossible as a long term storage and documentation of the original dosimeters. Finally, the behavior of a photographic film in the present context does not correspond to the behavior of organic tissue being subjected to an irradiation.
Therefore, conventional film dosimeters have increasingly been replaced by so-called alanine dosimeters. In this type of dosimeter, the dosimeter substance consists of alanine, i.e. an amino acid, the behavior of which, for example with respect to gamma rays, corresponds to that of organic tissue to a far more extent as is the case for conventional film dosimeters. In the art, alanine dosimeters are, therefore, referred to by the term xe2x80x9ctissue equivalentxe2x80x9d. Alanine, moreover, is very stable over an extended period of time, so that irradiated alanine may be again measured after a long period of time has lapsed, without any information having gone lost. Typically, doses of irradiation of interest in the present context are within the range of between 400 Gy (Gray) and 100 kGy (Kilogray).
As already mentioned above in connection with a standard established in the U.S., alanine dosimeters are conventionally measured and evaluated by utilizing the technique of electron paramagnetic resonance (EPR), also referred to as electron spin resonance (ESR). This is because when alanine is irradiated, so-called xe2x80x9cfree radicalsxe2x80x9d are generated, which, in the course of an ESR measurement, show a characteristic spectrum in which the amplitude of the primary line within the spectrum is representative for the dose of irradiation.
Document DE 196 37 471 C2 discloses a dosimeter substance, an alanine dosimeter as well as a method for their production. In this context it is disclosed that alanine dosimeters may be configured for utilizing pill- or film-shaped alanine elements of various geometry.
Document DE 39 03 113 C2 discloses a dosimeter as used for persons working in an irradiation-protected area. Likewise, alanine pills are used as dosimeter substance. The dosimeter itself consists of a small frame-shaped assembly having a corresponding chamber for receiving the alanine pills.
Document JP 02 173 589 A discloses still another dosimeter which is adapted to be evaluated by means of ESR. The dosimeter substance in that case has the shape of a strip and is applied to a small frame-shaped assembly.
Document JP 01 138 484 A mentioned at the outset, discloses a probe feed apparatus for ESR dosimeters. In this prior art apparatus, rod-shaped dosimeter elements are inserted into corresponding, axially extending recesses within a rotating disc, the rotation of which is controlled by means of optical sensors. The rotating disc is located above an ESR sample chamber. By rotating the disc accordingly, various dosimeter elements may be positioned above the ESR sample chamber one after the other and may then be lowered thereinto, where they are held in a reference position by means of appropriate holding elements.
Pressurized air may be fed to the sample chamber from its lower side in order to be able to blow the dosimeter element out of the sample chamber after completion of the ESR measurement.
During an ESR measurement, the ESR signal is measured as an electric mistuning of a resonator housing the sample under investigation. During the resonance transition, the sample absorbs energy and, hence, the resonator, having been tuned before, becomes mistuned. For that purpose, the external magnetic field acting on the resonator is conventionally swept slowly so that depending on the sample material and the complexity of the ESR spectrum, one or more resonance lines are generated.
Classical ESR spectrometry is limited in this context to the analysis of the particular appearance of the spectrum, i.e. the number, position and shape of the spectral lines which are recorded and analyzed. Although signal intensity plays a certain roll in that regard, conventional ESR spectrometers do not allow to measure signal intensity in absolute values. The reason is that the signal amplitude as an absolute value does not only depend on process parameters which may be set reproducibly, for example microwave frequency, the irradiated microwave energy, the scanning modulation amplitude, etc., but also from the type of sample, in particular its dielectric losses, the resonator tuning, the type of resonator used, etc.
In contrast, ESR dosimetry requires that the signal of the sample comprising the dosimeter substance be determined absolutely, namely with an accuracy of between 1 and 2%. This is impossible with conventional ESR spectrometers.
In another area of magnetic resonance, namely in the area of nuclear resonance (NMR), it is known to measure absolute signal amplitudes by concurrently measuring the sample under investigation and a so-called xe2x80x9cstandardxe2x80x9d, for example tetramethylsilane (TMS). These xe2x80x9cstandardsxe2x80x9d may either be mixed with the sample under investigation (so-called xe2x80x9cinternal standardxe2x80x9d), or they may be arranged separately within the probehead (so-called xe2x80x9cexternal standardxe2x80x9d), as the case may be. If the resonance behavior and, in particular, the amplitude of the reference material signal is predetermined, then the signal of the sample under investigation may be calibrated by comparing amplitudes.
In the context of investigations of solids, in particular of doped solids by means of electron spin resonance, one has to a large extent also made investigations on magnesium oxide with various dotations or contaminations, respectively, for example electron spin resonance of Cr3+ in MgO. In that context one has also investigated substances in which the chromium ions were present as the isotope 53Cr. In that case, an isotopic spectrum with particular hyperfine structure was obtained, i.e. a structure having a plurality of spectral lines.
It is, therefore, an object underlying the present invention to improve a probehead of the type specified at the outset, such that the afore-mentioned disadvantages are avoided.
In particular, the invention shall make it possible to provide a probehead for an ESR dosimeter allowing a processing of irradiated dosimetry strips in a faster and safer way. In particular, it shall become possible to individually identify dosimeter strips so that a proper documentation of the measurement results is possible, as is described for certain certification processes.
Still another object underlying the invention is to enable measurements of absolute values quickly and easily so that the irradiation dose may be reliably measured and documented.
According to another object underlying the invention, an ESR dosimeter shall be provided allowing to process irradiated dosimeter pills quickly and safely, wherein also a manual supply of dosimeter pills to the probehead shall be possible, even by non-skilled persons.
Finally, it is an object underlying the present invention to provide a sample substance of the type specified at the outset such that the afore-mentioned disadvantages are avoided.
In particular, the invention shall enable to provide a reference substance for the electron spin resonance dosimetry having only one single characteristic line within the ESR spectrum having a sufficient distance from the resonance of the free electron (g=2) and the ESR behavior of which corresponding essentially to the behavior of the sample under investigation containing the dosimeter substance.
These and other objects are achieved according to the present invention by a probehead for an electron spin resonance dosimeter, comprising a resonator, and an insert extending into the resonator and having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, wherein the guide channel is configured for receiving and guiding a test strip.
By guiding the test strip, the test strip will always be located at a predetermined reference position during the ESR measurement so that the measurement is made under reproducible conditions. This enables faster and safer measurements.
In a preferred embodiment of the inventive probehead, the test strip consists of a carrier material, and the carrier material is coated with the dosimeter substance at least over a section thereof.
This measure has the advantage that the test strip may be utilized for various functions.
This holds true in particular when, according to a further embodiment of the invention, the test strip is provided with a first machine-readable code imprint.
This measure has the advantage of a reliable identification of any test strip with conventional means, for example with a commercially available bar code reader.
It is particularly preferred in that context when, further, the insert is provided with a second machine-readable code imprint.
This measure has the advantage that not only each individual test strip may be automatically identified. Moreover, the particularly used test strip may be allocated to the particularly used insert so that the ESR measurement may be documented extensively.
For that purpose, it is preferred when the code imprints are located side by side when the test strip is inserted into the guide channel, wherein the insert is configured optically transparent at least in the area of the first code imprint.
This measure has the advantage that both code imprints may simultaneously be read by means of the same optical reader. Insofar, compact structures become possible.
According to still another preferred embodiment of the invention, the first code imprint is readable by means of a code reader only when the test strip is in a predetermined position and in a predetermined orientation within the guide channel.
For that purpose, the optically transparent area is located such that the first code imprint can be read only when the test strip is in a predetermined position and in a predetermined orientation within the guide channel.
According to still another embodiment of the invention, the guide channel is provided with a stop for the test strip which can preferably be configured by the lower terminal end of the vertically extending guide channel.
These measures have the advantage, that measurements may be executed extremely simply by manually feeding the insert with test strips. The user of the inventive probehead needs only to insert the test strip from above into the guide channel. When the guide channel extends vertically, the test strip will fall downwardly under the action of gravity, until it comes to rest at the stop with its lower terminal end, namely at the lower bottom of the guide channel. In any event, the test strip has then assumed its predetermined reference position within the probehead.
The above approach may still further be improved as well for manual as well as for automatic operation when the guide channel is provided with an insertion assisting means for the test strip.
According to further embodiments of the invention, the insert is provided with at least one reference sample, the reference sample being positioned within the insert such that it is located in the area of the section coated with the dosimeter substance, when the test strip is inserted into the guide channel.
This measure has the advantage that absolute measurements on test strips become possible because the signal intensity of the dosimeter substance comprised in the measuring sample may be converted into absolute values when their signal is compared to the predetermined signal of the reference sample and an appropriate ratio is computed.
Within the scope of the present invention, it is particularly preferred to use alanine as dosimeter substance.
The objects underlying the invention are, further, solved by a probehead for an electron spin resonance dosimeter, comprising a resonator, and an insert extending into the resonator and having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, wherein the insert is provided within a first machine-readable code imprint.
If, namely, the insert is provided with a corresponding code imprint, various information may be detected during the measurement and may be stored together with the measurement result of the measuring probe. This type of information comprises, for example, information about the type, size, etc. of the particularly used insert, information about ESR spurious or base signals coming from the insert and being unavoidable to a certain extent, which signals will also be generated during the later ESR measurement but can be eliminated from the measurement on the measuring probe by appropriate computation if these spurious or based signals are known. Finally, the code imprint may provide information about a reference sample integrated into the insert.
In a preferred embodiment of the invention, a code reader is associated to the first code imprint.
This measure has the advantage that commercially available instruments may be used at low cost.
In a further embodiment of the invention, the sample is provided with a second machine-readable code imprint.
This measure has the advantage that not only characteristic values of the insert but also values of the sample itself may be read prior to the measurement and correspondingly stored. This allows a still more complete documentation of any parameters possibly influencing the measurement.
The object underlying the invention is further solved by a probehead for an electron spin resonance dosimeter, comprising a resonator, and an insert extending into the resonator and having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, wherein the insert is provided with at least one reference sample.
By utilizing a reference sample with an ESR signal of predetermined amplitude, the absolute value for the measuring probe may be determined by comparing the ESR signal of the reference sample on the one hand and of the measuring probe comprising the dosimeter substance, on the other hand. Therefore, via measuring the reference sample, the dose of the irradiation exerted on the measuring sample may be determined with sufficient precision of, for example, 1 to 2%.
In a preferred embodiment of the inventive probehead, the reference sample is positioned within the insert such that it is located in the area of the volume of the sample to be measured, when the sample is inserted into the guide channel.
This measure has the advantage that the measuring conditions become reproducible because the measuring sample on the one hand and the reference sample on the other hand are located at approximately the same location within the probehead and, hence, within the resonator, so that the measuring conditions for both samples are practically identical.
This holds true in particular when the guide channel extends vertically within the insert, and a stop for the sample is provided at the lower terminal end of the guide channel, and the reference sample is arranged in the area of that stop.
This measure enables in particular to feed the inventive probehead with the dosimeter substance manually because it must only be inserted from above into the guide channel for then automatically falling downwardly under the action of gravity into the area of the stop. This corresponds to a precise reference position.
In this context, it is further preferred when the reference sample generates an ESR signal having a spectral position distant from the ESR signal of the dosimeter substance.
This measure has the advantage that both signals may be clearly separated one from the other and, hence, both signals may be evaluated without interfering with each other.
It is, further, particularly preferred when the reference sample generates an ESR signal having a microwave saturation behavior corresponding to the microwave saturation behavior of the dosimeter substance. The same applies, mutatis mutandis, for the line width, i.e. the modulation saturation behavior, as well as for the temperature coefficient.
All these measures have the common advantage that with a similar ESR measuring behavior, no error is generated when the measuring conditions are altered which would result in different reactions for the measuring sample on the one hand and the reference sample on the other hand, if their behavior were different.
The object underlying the invention is, further, solved by a probehead for an electron spin resonance dosimeter, comprising a resonator, an insert extending into the resonator and having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, and a pressurized air unit for blowing the sample out of the resonator after completion of a measurement, wherein the insert has an opening on an upper side of the resonator, the opening being openly accessible for manually inserting dosimeter pills thereinto, the insert, further, being provided on the upper side with a pressurized air connector, the pressurized air connector being connected to an orifice via a pressurized air channel within the insert, the orifice being located within a lower, otherwise closed bottom of the guide channel.
With this assembly, even unskilled persons are in a position to insert irradiated dosimeter pills which are supplied to them into the openly accessible opening from which the pills are automatically, i.e. under the action of gravity, conveyed to their measurement position where they may then be measured automatically. After completion of the measurement, the measured dosimeter pills are then disposed off automatically by feeding pressurized air and may, accordingly, be guided to a collecting means in which the dosimeter pills are, for example, packed, marked and documented.
As the probehead according to the present invention has all inputs, outputs and connectors located on the upper side of the resonator, the probehead may be utilized on commercially available ESR resonators, without the need of modifying the resonator or even the magnet system in which the resonator is located. Moreover, the guide- or convection system for the samples is closed in itself, so that the interior of the resonator is protected against ingression of dust.
According to a preferred embodiment of the invention, the guide channel has a rectangular cross-section.
This measure has the advantage that a form-fitting guide for the dosimeter pills is provided within the channel so that reproducible measuring conditions may be guaranteed.
This holds true in particular when the opening is configured as a slot.
This has the advantage that the dosimeter pills fed to the insert become oriented already during their insertion into the opening being openly accessible from above.
According to still another improvement of the invention, the opening is arranged at a lateral distance from the guide channel, and has a transition to the guide channel via a chamfered guide means.
This measure has the advantage that the opening is very well accessible laterally so that dosimeter pills may be fed manually without problems. The chamfered guide in the transition between the opening in the guide channel guarantees that the dosimeter pills will not become stuck but will safely come to their measurement position.
In still another group of embodiments, the guide channel has an upper end and a transition into a blow-out channel at the upper end, in particular a 180xc2x0 elbow.
These measures have the advantage that the trajectory of the blown-out dosimeter pills is well-defined. Further, the flush arrangement between the guide channel and the blow-out channel has the advantage that the dosimeter pills will safely fly from the guide channel into the blow-out channel during the blowing-out.
Furthermore, certain embodiments of the invention preferably provide for a reference sample located essentially at the bottom of the insert, wherein also two reference samples with distinct gyromagnetic ratios may be provided essentially at the bottom.
This measure has the advantage that quantitative measurements, i.e. calibrated amplitude measurements, may be conducted on the dosimeter pills.
The object is, finally, also solved by a sample substance for an electron spin resonance dosimeter, comprising a chromium-doped magnesium oxide (Cr:MgO), wherein the magnesium oxide is doped with an isotope 52Cr.
In the context of the present invention, one has, namely, surprisingly found that 52Cr:MgO has only one single explicit ESR resonance line being sufficiently distant from g=2 and, further, having ESR properties corresponding essentially to those of the conventional dosimeter substance alanine. This relates to a comparable line width (i.e. modulation saturation behavior), a comparable microwave saturation behavior, a comparable temperature coefficient, an isotropic behavior, etc.
Although the pertinent literature has already reported on ESR investigations on chromium-doped magnesium oxide, one has never found on Cr:MgO nor on 53Cr:MgO, also described in the literature, that an ESR spectrum has one single explicit line. In contrast, one has measured an explicit hyperfine structure, i.e. the exact contrary, on 53Cr:MgO. Moreover, it cannot be taken from the measurements described in the literature that chromium-doped magnesium oxide has similarities with alanine, i.e. an amino acid, for what concerns the ESR behavior.
In a preferred embodiment of the invention, the isotope 52Cr is used in an isotope-pure abundance ( greater than 95%).
Furthermore, it is preferred when the fraction of the isotope 52Cr within the doped magnesium oxide 52Cr:MgO is between 0.05 and 0.15%.
These values have shown to be very advantageous in practice.
In a nutshell, the invention comprises the use of 52Cr:MgO as a reference substance for the electron spin resonance dosimetry.
Further advantages will become apparent from the description and the enclosed drawing.
It goes without saying that the afore-mentioned features and those that will be explained hereinafter, may not only be used in the particularly given combination, but also in other combinations, or alone, without leaving the scope of the present invention.